1. Field of the Invention
This invention in general relates to fuel cell structures and assemblies, and more specifically to fuel cell structures and assemblies that comprise multiple microfibrous fuel cell elements arranged and constructed for efficient thermal and/or humidity management.
2. Description of the Related Art
In recent years, fuel cell or fuel cell assembly has become more and more available as a power source for use in handheld or mobile electrical devices, electrically powered vehicles, as well as in distributed power generation applications.
Fuel cells offer especially attractive prospects as energy conversion devices, by exhibiting high energy efficiency and low levels of gaseous/solid emissions, in comparison with traditional combustion-based energy sources.
In addition to generation of electrical energy, fuel cells convert a portion of the chemical energy stored in the fuel into heat during the electrochemical reaction, which, if efficiently collected and utilized, will significantly increase the overall energy (electrical+thermal) efficiency of the fuel cell systems. Therefore, there is an on-going interest in developing fuel cell systems as cogeneration systems for both electrical and thermal energy, to increase efficiency of such systems. The thermal energy produced by such cogeneration systems can be used for both heating and cooling (by using absorption or adsorption chiller or desiccant cooling), to support adjacent industrial facilities and domestic residences.
The thermal energy managing devices or structures used in conventional fuel cell cogeneration systems are usually very bulky in size, which include various heat exchanging panels, pipes, fluid pumps, and tubings, for which significant space is required, in additional to that of the fuel cell itself. There is therefore a need to provide a compact fuel cell system with thermal energy collecting/transferring components that are space-saving in character.
Further, in proton exchange membrane (PEM) fuel cells wherein continuous flow of feed (such as hydrogen or methanol) and oxidant (such as air or oxygen) is required for the electrochemical reactions therein, the feed or the oxidant stream needs to be sufficiently humidified to prevent drying of the membrane separators in the fuel cells. Humidifying devices or structures, such as water tanks, pumps, tubings and control devices, are therefore necessary for supplying water or water vapor to the fuel cell systems, in order to maintain the electrochemical reaction rate and the energy output density. Such humidifying devices or structures further increase the size of the fuel cell system. It will therefore be advantageous to provide a compact fuel cell system with reliable humidifying components having space-saving characteristics.
A recent innovation in the fuel cell industry is the development of microfibrous fuel cells, as described in details in U.S. Pat. Nos. 5,916,514; 5,928,808; 5,989,300; 6,004,691; 6,338,913; 6,399,232; 6,403,248; 6,403,517; 6,444,339; 6,495,281; all to Ray R. Eshraghi. Such microfibrous fuel cells are shaped as elongated fibers with very small cross-sectional diameters (ranging from a few hundred microns to a few millimeters), and can be serially and/or parallelly arranged, interconnected, and packed into compact fuel cell assemblies of very high voltage and power densities.
For thermal management in such microfibrous fuel cell assemblies, Eshraghi patents disclose use of hollow, fibrous heat exchanging tubes, which are packed side by side with the microfibrous fuel cells, and through which a coolant medium is passed for removing heat out of such fuel cell assemblies.
Eshraghi patents further disclose that such hollow, fibrous heat exchange tubes may comprise a water-permeable porous membrane wall, so that water deriving from an aqueous coolant medium permeates from the bores of such heat exchange tubes through the membrane wall into the feed stream, thereby humidifying the electrochemical reaction environment.
Therefore, the Eshraghi patents provide a compact fuel cell assembly with an integrated thermal and humidity management structure.
The present invention improves the thermal and/or humidity management efficiency in the Eshraghi fuel cell assembly, and advances the Microcell™ technology in the aspect of electrical and thermal energy cogeneration.
Other objects of the present invention will be more fully apparent from the ensuing disclosure and appended claims.